Inhibiting corticospinal excitability by entraining ongoing mu-alpha rhythm in motor cortex

Sensorimotor mu-alpha rhythm reflects the state of cortical excitability. Repetitive transcranial magnetic stimulation (rTMS) can modulate neural synchrony by inducing periodic electric fields (E-fields) in the cortical networks. We hypothesized that the increased synchronization of mu-alpha rhythm would inhibit the corticospinal excitability reflected by decreased motor evoked potentials (MEP). In seventeen healthy participants, we applied rhythmic, arrhythmic, and sham rTMS over the left M1. The stimulation intensity was individually adapted to 35 mV/mm using prospective E-field estimation. This intensity corresponded to ca. 40% of the resting motor threshold. We found that rhythmic rTMS increased the synchronization of mu-alpha rhythm, increased mu-alpha/beta power, and reduced MEPs. On the other hand, arrhythmic rTMS did not change the ongoing mu-alpha synchronization or MEPs, though it increased the alpha/beta power. We concluded that low intensity, rhythmic rTMS can synchronize mu-alpha rhythm and modulate the corticospinal excitability in M1. Highlights We studied the effect of rhythmic rTMS induced E-field at 35 mV/mm in the M1 Prospective electric field modeling guided the individualized rTMS intensities Rhyhtmic rTMS entrained mu-alpha rhythm and modulated mu-alpha/beta power Arrhythmic rTMS did not synchronize ongoing activity though increased mu-alpha/beta power. Rhythmic but not arrhythmic or sham rTMS inhibited the cortical excitability in M1